A multispectral image is an image captured using light having at least two different wavelength spectra or an image captured using light having at least two different polarization states.
Examples of a multispectral image include images captured using light having three wavelength spectral characteristics, namely, an image captured using light having a first spectral characteristic that indicates a distribution of components at a wavelength of about 700 nm, an image captured using light having a second spectral characteristic that indicates a distribution of components at a wavelength of about 546 nm, and an image captured using light having a third spectral characteristic that indicates a distribution of components at a wavelength of about 435 nm. This multispectral image is a color image represented by so-called RGB three primary colors.
Other than the above, imaging with light having two or more spectral characteristics (infrared rays and visible light, for example) is now used in the industrial and medical fields, for instance.
Some methods have already been disclosed with the aim of capturing a multispectral image.
The first method is a method in which filters with different transmission properties are disposed immediately above and in one-to-one correspondence with light receiving elements in a two-dimensional light receiving element array. This method is widely used in, for instance, digital cameras which can capture color images.
The second method is a method in which a filter group including plural filters with different transmission properties and a separation optical element are disposed in an imaging optical system. The separation optical element has a function of distributing bundles of rays which have passed through the filters so that the distributed bundles of rays enter different light receiving elements in a two-dimensional light receiving element array.
Patent Literatures (PTLs) 1 and 2 disclose the second method in detail. The second method limits the position for disposing the filter group. The filter group is disposed at a stop position in PTL 1 and at a pupil position in PTL 2.